JP5816046B2 - A method of storing bit-wise holographic data in parallel using a parallel light source - Google Patents

Description

  The present technology generally relates to bit-wise holographic data storage technology. More specifically, the present technology relates to a method and system for performing parallel replication of holographic disks.

  As computing performance has advanced, computing technology has entered new applications such as consumer video, data storage, document storage, image processing, and movie production, among others. These applications have driven the development of data storage technologies that increase storage capacity and data rate.

  One example of the development of data storage technology may be the innovatively large storage capacity of optical storage systems. For example, compact discs developed in the early 1980's have a capacity of about 650-700 MB of data, or about 74-80 minutes of 2-channel audio program. In contrast, the digital versatile disc (DVD) format developed in the early 1990s has a capacity of about 4.7 GB (single layer) or 8.5 GB (double layer). In addition, larger storage capacity technologies have been developed to meet greater demands, such as the demand for higher resolution video formats. For example, a mass storage format such as the Blu-ray Disc ™ format can hold approximately 25 GB on a single layer disc or 50 GB on a dual layer disc. As computing technology continues to advance, storage media with greater capacity may be desired. For example, holographic storage systems and micro-holographic storage systems are examples of other advanced storage technologies that can achieve capacity increasing requirements in the storage industry.

  Holographic storage is holographic data storage that is an image of a three-dimensional interference pattern created by the intersection of two light beams in a photosensitive storage medium. We have pursued both page-based holography technology and bit-wise holography technology. In page-based holographic data storage, a signal beam containing digitally encoded data (eg, multiple bits) is superimposed with a reference beam within the volume of the storage medium that results in a chemical reaction, Modulates the refractive index of the medium within this volume. Thus, typically each bit is stored as part of the interference pattern. In bit-wise holography or microholographic data storage, all bits are written as micro-holograms or Bragg reflection gratings, usually generated by two recording back-propagating focused beams. The data is then retrieved by using a read beam that reflects off the micro-hologram to reconstruct the recording beam.

  Bit-wise holography systems allow the recording of microholograms that are focused in layers in a smaller space, and thus can provide significantly greater storage capacity than conventional optical systems. However, the bandwidth of a bit-wise holography system can be limited by the transmission speed of one transmission channel and the rotational speed of the holographic storage disk. For example, the normal disk rotation speed of a Blu-ray ™ system may be about 430 Mbit / s single channel transmission at 12 times BD speed. At this transmission speed, the recording time per data layer of the disc is about 500 seconds. Techniques that increase the transmission rate of bit-wise microholography systems can be effective.

US Patent Application Publication No. 2009/0147333

  Embodiments of the present technology provide an optical device having a plurality of optical fibers configured to transmit and output a plurality of light waves to a set of focusing elements. The set of focusing elements is configured to receive a plurality of light waves output by the plurality of optical fibers and configured to focus the plurality of irradiation spots onto the holographic disk. Each irradiation spot of the plurality of irradiation spots is located on one of the plurality of data tracks in the holographic disk.

  Another embodiment provides an optical device configured to transmit and output a plurality of light waves. The optical device includes a first set of optical elements and a second set of optical elements. The first set of optical elements is configured to receive a plurality of light waves output by a plurality of optical fibers, and from one side of the disk, the plurality of light waves are directed to a plurality of first light spots in the holographic disk. Constructed to focus, each light spot of the plurality of first light spots is located on one of the plurality of data tracks in the optical disc. The second set of optical elements is configured to receive a plurality of light waves output by a plurality of optical fibers, and from the other side of the disc, the plurality of light waves are directed to a plurality of second light spots in the holographic disc. The light spots are configured to converge, and each light spot of the plurality of second light spots overlaps with a corresponding light spot of the plurality of first light spots to form a hologram.

  Another embodiment provides a method for recording and reading micro-holograms on parallel data tracks in a holographic disk. The method includes providing an optical fiber bundle in the optical system. The optical fiber bundle includes a plurality of optical fibers, and the optical fiber bundle is configured to form a focused spot in the holographic disk. The method further includes adjusting one or more elements in the optical system such that a focused spot is formed on the plurality of data tracks.

  These and other features, aspects and advantages of the present invention will be more fully understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings.

1 is a diagram showing an optical disc having a data track according to an embodiment. FIG. 1 is a block diagram of a microholographic replication system according to an embodiment. FIG. FIG. 6 is a schematic diagram comparing a single beam replication technique and a multiple parallel beam replication technique according to an embodiment. 1 is a schematic view of a multi-head system for recording in parallel on a plurality of tracks of a holographic disk according to an embodiment. FIG. FIG. 2 is a schematic diagram of a single head transmitting multiple beams that are recorded in parallel on multiple tracks of a holographic disk according to one embodiment. FIG. 3 is a cross-sectional view illustrating various types of polarization maintaining optical fibers (PMFs) according to an embodiment. 2 is a schematic side view of a plurality of light waves incident on a holographic disc according to an embodiment. FIG. FIG. 8 is an enlarged schematic view of FIG. 7 illustrating interference in a holographic disc according to an embodiment. FIG. 3 is a cross-sectional view of a plurality of PMFs configured to transmit a plurality of light beams in which polarized light according to an embodiment is aligned in one direction. 2 is a cross-sectional view of a plurality of PMFs configured to transmit a plurality of light beams with alternating polarizations according to an embodiment. FIG. 2 is a cross-sectional view of a plurality of PMFs configured to transmit a plurality of light beams at one wavelength and different spatial coherence according to an embodiment. FIG. FIG. 3 is a cross-sectional view of a plurality of PMFs configured to transmit a plurality of light beams having different spatial coherence and different wavelengths according to an embodiment. 2 is a cross-sectional view of a plurality of PMFs configured to fit into a grooved fixture in accordance with an embodiment. FIG. It is the schematic which shows the one-dimensional fiber array which inclines according to the track pitch of the holographic storage medium based on an embodiment. It is the schematic which shows the two-dimensional fiber array which inclines according to the track pitch of the holographic storage medium based on an embodiment.

  One or more embodiments of the present technology are described below. In an effort to provide a concise description of these embodiments, the specification does not describe all features of an actual implementation. As with any engineering or design project, the development of any such actual embodiment is specific to the developer, such as following system-related and business-related constraints that may vary from embodiment to embodiment. It should be understood that in order to achieve the objective, a judgment according to many embodiments needs to be made. Moreover, such development efforts can be complex and time consuming, but it will be understood by those skilled in the art who benefit from this disclosure that they are routine tasks of designing, processing, and manufacturing. .

  Bitwise holographic data storage systems typically involve recording by emitting two superimposed interference beams in a recording medium (eg, a holographic disk). When illuminated by a focused beam, data bits are represented by the presence or absence of a microscopic sized localized holographic pattern called a micro-hologram that acts as a volumetric mirror. For example, the holographic disk 10 shown in FIG. 1 represents how data bits can be organized in that layer. Typically, the holographic disk 10 is a flat circular disk that includes one or more data storage layers embedded in a transparent plastic coating. The data layer can include a number of surfaces that can reflect light, such as micro-holograms used for bit-wise holographic data storage. In some embodiments, the data layer can include a holographic recordable material that is responsive to a strong illumination light beam striking the disk 10. For example, in various embodiments, the material of the disk 10 can be threshold responsive or linear responsive. The data layer can be between about 0.05 μm and 5 μm thick and can have a spacing between about 0.5 μm and 250 μm.

  Data in the form of micro-holograms can usually be stored in a continuous spiral track 12 from the outer edge of the disk 10 to the inner limit, although concentric circular tracks or other configurations can be used. it can. The main shaft hole 14 can be sized to engage about the main shaft of the holographic system, allowing the disk 10 to be rotated for data recording and / or reading.

  A general system for recording micro-holograms on the holographic disk 10 is provided in the block diagram of FIG. The holographic system 16 includes a light source 18 that can be split into a signal beam 20 and a reference beam 22. As will be described, in one embodiment, the light source 18 (which may be a single light source or multiple light sources) may emit a plurality of parallel light beams that are recorded on parallel tracks 12 of the disk 10. it can. The parallel light source beam can also be split into a parallel signal beam 20 and a parallel reference beam 22. The signal beam 20 can be modulated in response to data to be recorded on the disk 10 (block 24). In certain embodiments, the processor 40 may control the modulation of the signal beam 20 (block 24). The modulated signal beam 26 can pass through an optical element and servo mechanism system 28, which can be configured to focus the focused signal beam 30 to a specific location on the disk 10. Optical and servomechanism devices can be included. For example, the optical element and servomechanism system 28 can focus the focused signal beam 30 onto a particular data layer or data track 12 of the disk 10.

  The reference beam 22 passes through an optics and servomechanism system 32 that includes various optics and servomechanism devices designed to focus the focused reference beam 34 onto a particular data layer or data track 12 of the disk 10. The focused reference beam 34 overlaps the focused signal beam 30. The micro-hologram can be recorded in the irradiation spot of the interference pattern formed by the two overlapping back-propagating focused laser beams 30 and 34 in the holographic disk 10. In some embodiments, the recorded micro-hologram can be retrieved from the disk 10 using the focused reference beam 34. The reflected light of the focused reference beam 34, referred to as data reflected light 36, can be received at a detector 38 for signal detection.

  A plurality of successive micro-holograms are placed on the track 12 of the disk 10 by holding the overlapping back-propagating focused beam on the desired track as the disk 10 is rotated about the main axis disposed through the main shaft hole 14. Can be recorded. Usually, some degree of back-propagating beam superposition is maintained to accurately and reliably record micro-holograms on the appropriate tracks 12 and / or layers of the holographic disk 10. Optical and servomechanism systems 28 and 32 can be utilized to dynamically maintain the desired overlap by disk rotation during the micro-hologram recording process.

  Such optical and servomechanism elements 28 and 32 may increase the complexity of the end user device recording on the holographic disk 10. The present technology provides a method and system for pre-creating a holographic disc 10 with micro-holograms so that the disc 10 can be modified and / or erased by an end user device using single beam exposure. Pre-creation of the holographic disk refers to recording a micro-hologram during the manufacturing process of the holographic disk 10. Microholograms recorded during the pre-creation process can represent codes, addresses, tracking data, and / or other ancillary information. The pre-recorded micro-hologram can be subsequently modified and / or erased using a single beam rather than a superimposed back-propagating beam. Thus, the end-user system does not need to hold the overlapping back-propagating laser beam to record data on a pre-made holographic disk. Instead, end-user systems that use a single beam can be used to record, modify, and / or erase micro-holograms on pre-made holographic discs.

  While recording a micro-hologram with a back-propagating beam to pre-create a holographic disk can reduce the complexity of changing the micro-hologram of the end-user device, the process of pre-creating the disk is It can also be improved. As explained, when the holographic disc 10 is pre-created, the disc 10 may record a micro-hologram on a selected track 12 and / or layer of the disc 10 with a superimposed backpropagating beam directed to the disc 10. Rotates in the holographic system so that it can. The rotational speed of the disk 10 limited to some extent by the mechanical strength of the disk material limits the recordable speed (referred to as transmission speed) of the micro-hologram. For example, the normal disc rotation speed of Blu-ray Disc ™ may be a transmission speed of a one-channel system of about 430 megabits / second at a 12 times BD speed. At this transmission speed, the recording time per data layer of the disc is about 500 seconds.

  In one or more embodiments, parallel micro-hologram recording techniques can be used to increase the transmission speed of the holographic disk 10 and reduce its recording time. For example, parallel micro-hologram recording can include directing multiple beams to a holographic disk to illuminate multiple tracks 12 of the disk 10. A beam can refer to collecting light propagating in approximately the same direction through the same set of optical elements and can include light emitted from various light sources. Multiple beams (from the opposite direction) so that multiple overlapping back-propagating beams can form an interference pattern of multiple illumination spots, resulting in multiple micro-holograms recorded in parallel tracks 12 of the disk 10. That is, the back-propagating beam can be guided to a plurality of tracks 12 of the disk 10. Further, in some embodiments, the overlapping beams can interfere at a focused spot having a relatively small area in the data layer plane. The concentrated irradiation spot of the interference pattern can be separated by a non-irradiation region. By limiting the illuminated area on the data layer, the deep area of the recorded micro-hologram can be limited to the desired size and / or limited to the desired data layer (eg, about 0.05 μm to 5 μm). ).

The schematics of FIGS. 3A and 3B compare two different approaches for recording micro-holograms in parallel. In FIG. 3A, wide range illumination using the single beam approach 42 includes using a single beam 44 to illuminate a relatively wide range within the master disk 46 (eg, across multiple data tracks 12). . The master disk 46 can contain data to be replicated on the replica disk 10 and a wide range of multiple data tracks 12 can simultaneously replicate data on the multiple data tracks 12 by a single beam 44. The reflected light 48 from the master disk 46 can pass through a light imaging system 50, represented as a lens in FIG. 3A, which focuses the reflected light 48 and produces a focused reflected light 52. It can be led to the duplicate disk 10. A single wide-range reference beam 54 can also be directed to the opposite side of the replica disk 10 so that the focused reflected light 52 and the reference beam 54 can back propagate, interfere, and form a hologram pattern 56. The duplicate disk 10 can have a plurality of data layers represented by vertical lines L ₀ , L ₁ , and L ₂ .

However, an increase in the field of view of the single beams 44 and 54 typically results in an increase in the deep area of the hologram recorded in the duplicate disk 10. The deep area increase characteristic can refer to an increase in the size of the hologram that penetrates the greater thickness of the disk 10 (in the direction of the single beams 44 and 54) and may penetrate multiple layers. For example, when both single beams 44 and 54 can be directed to layer L ₁ , linear materials typically used in such page-based wide-area illumination systems are relatively sensitive to a wide illumination range. It is possible that the material of the adjacent layers L ₀ and L ₂ may be affected by the single beams 44 and 54. Accordingly, since the recording of one holographic pattern may require a plurality of data layers, the increase in the deep area in the holographic recording may limit or reduce the data capacity of the holographic disk 10.

  One embodiment of the present technology is illustrated in the multiple parallel beam technique 58 of FIG. 3B. Rather than illuminating a relatively wide area with a single beam, as in the single beam technique 42 of FIG. 3A, the multiple parallel beam technique 58 involves directing multiple back-propagating parallel beams to the holographic disk 10. In one embodiment, a plurality of parallel signal beams 60 are directed to the master disk 46, and the reflected light 62 from the master disk 46 can pass through the optical imaging system 50, represented as a lens in FIG. 3B. The optical imaging system 50 can focus the reflected light 62 and direct the focused reflected light 64 to the replica disk 10.

A plurality of parallel reference beams 66 can also be directed to the opposite side of the disk 10. In some embodiments, the parallel reference beam 66 and the parallel signal beam 60 can be split from a common parallel channel light source 18 (FIG. 2), and in some embodiments, the parallel reference beam 66 and the parallel signal beam 60 can be Can be transmitted from any light source. The parallel reference beam 66 and the focused reflected light 64 can propagate back and interfere to form an interference pattern on the data layer (eg, data layer L ₁ ) of the disk 10. The interference pattern can include a plurality of illuminated spots separated by non-irradiated areas (eg, each spot can correspond to one interference of a pair of back-propagating parallel beams). Each of the interference spots can form a micro-hologram 68 in the data layer L ₁ . Since only a small portion of the data layer plane is irradiated to the entire area of the data layer plane of the data layer L _{1 (} not the wide area in the single beam technique 42), the beam spot (or micro-hologram) of the irradiation pattern is irradiated. 68) can be relatively focused in _one data layer L1, which can increase the data capacity of the disk 10.

  In some embodiments, using multiple parallel beams for parallel micro-hologram recording may utilize multiple optical heads as shown in FIG. The optical head 70 can irradiate a single beam, and a plurality of optical heads 70 in the replication system 16 (eg, FIG. 2) are positioned so that the beam 60 impinges on the data track 12 of the disk 10, respectively. The plurality of beams 60 irradiate the plurality of tracks 12 in parallel. In certain embodiments, each optical head can have a separate optical element configured to focus the beam 60 onto the track 12. Further, an additional set of optical heads can be configured to strike the disk 10 from opposite directions, so that the parallel beam 60 emitted from each optical head 70 is back-propagated and data in one layer of the disk 10 is transmitted. Interference is made at the track 12. In certain embodiments, the optical head 70 can include one or more dove prisms, pentaprisms, or other optical elements.

  In another embodiment shown in FIG. 5, parallel micro-hologram recording using multiple parallel beams can utilize an optical head 72 that transmits multiple light beams 60 in parallel from a set of optical elements. In one embodiment, multiple parallel signal beams 60 from a single optical head 72 can be transmitted through a bundle of individual fibers suitable for transmitting the light beam, with each beam being an optical head. When transmitted from 72 to a plurality of tracks 12 of the disk 10, it is made discrete. As will be described, the optical head 72 includes imaging optics configured to reduce the illumination pattern formed on the data plane (eg, one or more data layers of the disk 10) by the plurality of beams 60. Or it can be coupled to the imaging optics. Reduction of the irradiation pattern may increase the probability that each irradiation spot is recorded on the data track 12 of the disc. In certain embodiments, the optical head 72 may include a dove prism, a pentaprism, or other optical element. By transmitting a back-propagating parallel beam 66 from another optical head 74 having another bundle of individual fibers from the opposite side of the disk 10, or the parallel beam (as discussed with respect to FIG. 2) and the signal beam 60 and reference By splitting the beam 66, a back-propagating parallel signal beam 60 can be obtained.

  In one or more embodiments, a bundle of individual optical fibers can be used to transmit multiple beams (ie, light waves) to the holographic disk 10. For example, the fiber bundle can output light waves through multiple optical heads 70, or a single optical head 72, suitable for transmitting multiple beams 60. The fiber bundle can include a plurality of optical fibers, such as single mode fibers. In some embodiments, the fiber bundle can include a plurality of polarization maintaining optical fibers (PMF or PM fibers). PM fiber is an optical fiber in which the polarization of a linearly polarized light wave transmitted through the fiber is maintained during the propagation of the light wave. In certain embodiments, a recording or backpropagating light wave can propagate through each PM fiber to pre-record microholograms on the disk 10. The light wave is usually polarized by a polarizing element before being launched into the PM fiber, and depending on various factors such as temperature and stress in the PM fiber, the polarization of the polarized light wave is removed from the input of the PM fiber. The output part can be almost held.

  FIG. 6 shows cross-sectional views of three examples of PM fibers that can be used in the present technology. PM fibers 76, 78, and 80 can each be designed to induce stress in fiber core 82. For example, PM fiber 76 may be similar to PandaPM fiber manufactured by Corning®, and PM fiber 80 may be similar to bowtie PM fiber manufactured by Fibercore®. There is. Other configurations and types of PM fibers can be used depending on the technology. Stress can be induced through various lengths of stress rod 84 aligned with the core 82 through the entire length of the PM fibers 76, 78, and 80. In certain embodiments, the applied temperature can result in thermal expansion of the stress rod 84 on the fiber core 82 that contributes to maintaining the polarization of the light waves propagating through the PM fibers 76, 78, and 80. is there.

  By pre-recording on the holographic disk 10 with a bundle of PM fibers having a plurality of PM fibers 76, 78, and 80, the pattern of the illuminated light spot is formed on the disk 10 and on the plurality of data tracks 12 of the disk 10. Can be recorded. As described, recording on multiple parallel data tracks 12 while the disk 10 is rotating increases the transmission rate and reduces the time required to pre-create or write data to the disk 10. However, the parallelism and physical accessibility of bundles of PM fibers 76, 78, and 80 can cause interference between adjacent channels of propagating light waves. FIGS. 7 and 8 show how interference can occur between adjacent channels. In FIG. 7, the parallel signal beam 26 can pass through the optical system 28 (eg, a lens) and the focused signal beam 30 can be directed toward the disk 10. The focused signal beam 30 can be focused on the plane of the disk 10 and written parallel to the micro-hologram.

  An enlarged view of FIG. 7 is shown in FIG. 8, and the focused signal beam 30 is focused on a plurality of irradiation spots 88 on the focal plane 86. Each of the plurality of illuminated spots 88 can represent a micro-hologram and can be focused on a different data track 12 of the disk 10. The focal plane 86 can represent one data layer or multiple data layers of the disc 10. As shown in FIG. 8, the beam 30 overlaps before focusing on a spot 88 on the focal plane 86 to form an interference region 90 in the disk 10. When the interference area 90 represented as a shadow area in FIG. 8 occurs in the disc 10, there is a possibility of crosstalk that may lead to a data error in a previously recorded layer. For example, if the interference region 90 occurs on a pre-recorded focal plane 92 (eg, a pre-recorded layer), data errors or erasure of data may occur on the focal plane 92.

  In certain embodiments, various polarization or wavelength control schemes can be used to minimize interference and / or crosstalk of parallel data channels. Such a technique is generally described in FIGS. In some embodiments, the PM fiber bundle 98 can include a plurality of PM fibers 96. As shown in FIG. 9, the polarizations 94 of the light waves propagating through each of the parallel PM fibers 96 can be aligned in one direction, and the crosstalk between the light waves is a light wave having a smaller coherence length (about 30 μm). Can be reduced by introducing it into one or more laser diodes that couple to the input of the fiber bundle 98. By reducing the coherence length of one or more of the light waves entering the fiber bundle 98, the probability of interference within the disk 10 can be reduced.

  In another embodiment, crosstalk between parallel data channels can be reduced by configuring adjacent light waves to be orthogonally polarized, as shown in FIG. The orthogonal output polarization 100 between the light waves of adjacent PM fibers 96 in the fiber bundle 98 can reduce interference of the output light waves on the disk 10. In certain embodiments, various light polarizing elements can be used to polarize light waves to generate orthogonal output polarization 100, and in certain embodiments, various types of PM fibers 76, 78, and 80 can be Depending on the polarization state of the parallel light waves in the fiber bundle 98, it can be used to maintain the polarization state. For example, PM fiber 76 can be used in one polarization direction, while PM fiber 78 can be used in another polarization direction.

In order to reduce interference of output light waves in the disk 10, the wavelength of light waves input through the PM fiber bundle 98 can also be controlled. For example, as shown in FIG. 11, a plurality of laser diodes input to the fiber bundle 98 can emit at the same wavelength (λ ₁ ) 102, and crosstalk between light waves causes light waves having a smaller coherence length. It can be reduced by leading to one or more of the laser diodes. By emitting light of the same wavelength through each of the PM fibers 96 and reducing one or more coherence lengths of the light waves, interference of the light waves output from the fiber bundle 98 can be reduced.

Furthermore, in another embodiment, crosstalk between parallel data channels can be reduced by configuring adjacent light waves to have various wavelengths, as shown in FIG. For example, a plurality of laser diodes can input light waves into the fiber bundle 98 at two or more wavelengths (λ ₁ and λ ₂ ) 104 to reduce interference of output light waves in the disk 10. As described in Equation (1) below, the coherence length of a light wave is affected by the wavelength separation between that light wave and the adjacent light wave. The greater the separation between the wavelengths of two adjacent light waves, the smaller the coherence length.

In various embodiments, the techniques described above for reducing crosstalk between parallel data channels can be used separately or in combination. For example, the fiber bundle 98 can be configured to transmit light waves having the same or different output polarization, coherence length, and / or wavelength. PM fibers 96 having various characteristics can be alternately arranged (eg, interleaved) in the fiber bundle 98. Further, each PM fiber 96 in the fiber bundle 98 can be configured to transmit light waves having a constant output polarization, coherence, and / or wavelength, or each PM fiber 96 in the fiber bundle 98 can vary. It can be configured to transmit light waves having various characteristics.

  In certain embodiments, techniques for pre-recording data in parallel on a holographic disk and / or recording data in parallel also include placing a plurality of laser spots, and therefore, each laser spot is recorded on the disk through a recording program. 10 on the data track 12. Controls the accuracy of multiple laser spots across multiple data tracks when the data track pitch is about 1.6 μm for CD discs, about 0.74 μm for DVDs, and about 0.3 μm for Blu-ray Disc ™ Sufficient measurement accuracy can be used to do this. In one or more embodiments, mounting structures can be used to control the placement of PM fibers 76, 78, and 80 within fiber bundle 98. One example of the mounting structure is the grooved structure shown in FIG. 13 that includes a grooved upper portion 106 and a grooved lower portion 108 that sandwich a plurality of PM fibers 96. Each of the grooved upper part 106 and the grooved lower part 108 has an inclined surface that holds the PM fiber 96 in place. In one embodiment, the center-to-center motion of adjacent PM fibers 96 can be limited to within about ± 0.25 μm. Since the fiber bundle 98 is reduced to about 1: 5 and guides the output light to the focal plane, the final position tolerance of the focal plane can be about ± 0.05 μm, and the tolerance is about 0.3 μm. Significantly less than Blu-ray Disc ™ track pitch.

  The spacing (i.e., pitch) between adjacent PM fibers 96 is typically about 20 to 250 [mu] m. However, the standard fiber bundle 98 pitch is significantly larger than the Blu-ray Disc ™ pitch (0.3 μm). In one or more embodiments, adjacent data tracks 12 in the holographic disk 10 can be recorded in parallel by rotating the fiber bundle 98. The rotation angle of the fiber bundle 98 can be adjusted to control (e.g., reduce) the spacing between the irradiation spots on the disk 10. For example, the relationship between the pitch of the PM fibers 96 in the fiber bundle 98, the rotation angle of the fiber bundle 98, and the pitch of the tracks 12 in the disk 10 can be expressed by the following equation (2).

Here, P _track is the pitch of the track 12 in the disk 10, P _bundle is the pitch of the PM fiber 96 in the fiber bundle 98, and θ is the angle at which the fiber bundle 98 rotates.

  In various embodiments, various holographic systems can include various spacings between data tracks 12. In accordance with the present technique, the fiber bundle 98 is rotated at various angles along the propagation of the beam propagating through the fiber bundle 98 to obtain the desired track spacing of the illumination spot output by the fiber bundle 98. Can do. Further, the opposite fiber bundle 98 can be rotated or configured to output a backpropagating light wave that sufficiently overlaps on the data track 12 in the data surface 86 from the opposite direction.

Rotating the fiber bundle 98 to form an illumination spot on the track 12 having a smaller track pitch is shown in FIG. In some embodiments, the fiber bundle 98 can be in the form of a one-dimensional array 112. This array 112 can have a fiber spacing of 127 μm and can be rotated by an angle θ of 30 ° to form an illumination spot 110 approximately along the track 12. The angle θ is based on the track pitch P _track , and a larger fiber bundle pitch P _bundle requires a larger rotation angle θ to form an illumination spot on the disk 10 having a smaller track pitch P _track. there's a possibility that.

  In some embodiments, the fiber bundle 98 can be in the form of a two-dimensional fiber array, as shown in FIG. The 2D fiber array 114 can have a fiber spacing of 80 μm. Since the 2D fiber array 114 can have a smaller track pitch than the 1D fiber array 112 described in FIG. 14, it can be rotated by a smaller angle θ of 2.5 °.

  In one or more embodiments, light transmitted through the fiber bundle 98 to the disk 10 or one or more data layers in the disk 10 is directed to an optical head that transmits multiple light waves (eg, optical head 72 in FIG. 5). Further focusing on the desired data track 12 can also be achieved by using coupled imaging optics. The optical head 72 is an imaging optical element configured to reduce an irradiation pattern formed by a plurality of beams output from the fiber bundle 98 on a data surface (for example, one or more data layers of the disk 10). Or can be coupled to the imaging optics. By reducing the size of the irradiation pattern, the probability of recording each irradiation spot on the data track 12 of the disc may increase. In some embodiments, the magnification, referred to as the image reduction ratio, for reducing the irradiation pattern compared to the prototype output from the fiber bundle 98 can be about 2: 1 to 10: 1.

  Although only certain features of the invention have been illustrated and described herein, many variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such variations and modifications that fall within the true spirit of the invention.

DESCRIPTION OF SYMBOLS 10 Holography disk 12 Data track 14 Spindle hole 16 Replication system 18 Light source 20 Signal beam 22 Reference beam 24 Signal modulation 26 Modulation signal beam 28 Optical element and servo system 30 Focused signal beam 32 Optical element and servo system 34 Focusing reference beam 36 Detection beam 38 Signal Detection 40 Processor 42 Single Beam Technique 44 Single Beam 46 Master Disk 48 Reflected Light 50 Optical Imaging System 52 Focused Reflected Light 54 Single Reference Beam 56 Microhologram 58 Multiple Parallel Beam Technique 60 Parallel Beam 62 Reflected Light 64 Focused Reflected light 66 Parallel reference beam 68 Micro hologram 70 Optical head 72 Optical head for transmitting a plurality of beams 74 Optical head for transmitting a plurality of beams 76 PM fiber 78 PM fiber 8 0 PM fiber 82 Fiber core 84 Stress rod 86 Focal plane 88 Irradiation spot 90 Interference region 92 Focal plane 94 Polarization 96 PM fiber 98 Fiber bundle 100 Polarization 102 Wavelength 104 Wavelength 106 Grooved upper part 108 Grooved lower part 110 Illuminated spot 112 Fiber array 114 Fiber array

Claims (8)

A holography system (16) for writing a bit-wise micro-hologram on an optical disc (10),
A light source (18) split into a plurality of signal beams (20) and a plurality of reference beams (22);
A plurality of multi-polarization maintaining optical fibers (76, 78, 80, 96) configured to transmit and output the plurality of reference beams (22);
The plurality of reference beams (22) output by the plurality of multi-polarization-maintaining optical fibers (76, 78, 80, 96) are received, and the output reference beams (22) are transmitted to the optical disc. A set of optical elements (32) configured to focus on a plurality of irradiation spots (88, 110) in (10), each irradiation spot (88) of the plurality of irradiation spots (88, 110). 110), a set of optical elements (28, 32) located on one of the plurality of data tracks (12) in the optical disc (10);
In order to perform recording using each micro-hologram for each irradiation spot (88, 110), a plurality of modulated signal beams (26) obtained from the plurality of signal beams (20) are supplied to each irradiation spot ( 88, 110) and an optical element and servo system (28) configured to focus.
A system (16) comprising:   The system (16) of claim 1, wherein the plurality of illuminated spots (88, 110) are substantially limited to a single data layer in the optical disc (10).   The system (16) according to claim 1 or 2, wherein the plurality of illuminated spots (88, 110) are distributed to a plurality of data layers in the optical disc (10).   The system according to any of the preceding claims, wherein the multiple polarization maintaining optical fibers (76, 78, 80, 96) are bundled together using a V-grooved structure (106, 108). (16). The plurality of polarization maintaining optical fibers (76, 78, 80, 96) are bundled together in a mounting member (98);
The mounting member (98) is rotatable along a beam propagation axis;
System (16) according to any of claims 1 to 4.   The system (16) according to any of the preceding claims, wherein the plurality of multi-polarization maintaining optical fibers (76, 78, 80, 96) are configured in a one-dimensional array (112).   The system (16) according to any of the preceding claims, wherein the plurality of multi-polarization maintaining optical fibers (76, 78, 80, 96) are configured in a two-dimensional array (114). The plurality of multi-polarization maintaining optical fibers (76, 78, 80, 96) are configured to transmit a plurality of light waves (102, 104) having a single coherence value. System (16) according to.